Manganese dioxide, fluorocarbon, and the like are typical of positive electrode active materials for lithium primary batteries and have already become practical. In particular, manganese dioxide has the advantages of good storage property and being inexpensive. Much effort has thus been made to use manganese dioxide as a positive electrode active material (see Patent Documents 1 and 2).
The following are also known: a manganese dioxide formed by treating, with an acid, an orthorhombic lithium-manganese composite oxide obtained by low-temperature firing at 350° C. to 450° C. (Patent Document 3), a manganese dioxide obtained by treating spinel type LiMn2O4 (Patent Document 4) with an acid, and a manganese dioxide obtained by treating LiMn2O4 with an acid and then firing the treated material (Non-Patent Document 1).
Furthermore, Patent Document 5 discloses manganese dioxide obtained by firing λ type manganese dioxide at a temperature of 250° C. to 400° C. Patent Document 6 discloses a manganese dioxide obtained by firing λ type manganese dioxide at a temperature of 150° C. to 450° C. Patent Document 7 discloses a composite oxide obtained by treating a spinel type composite oxide with an acid and then thermally treating the treated material at a temperature of 200° C. to 400° C.    Patent Document 1: Japanese Patent Application Laid-Open No. 3-80120 (claims and others)    Patent Document 2: Japanese Patent Application Laid-Open No. 3-254065 (claims and others)    Patent Document 3: Japanese Patent Application Laid-Open No. 3-122968 (claims and p. 2 and 3 and others)    Patent Document 4: Japanese Patent Application Publication No. 58-34414 (p. 1 and 2 and others)    Patent Document 5: Japanese Patent Application Laid-Open No. 61-17424 (p. 3 and others)    Patent Document 6: Japanese Patent Application Laid-Open No. 1-231270 (claims and others)    Patent Document 7: Japanese Patent Application Laid-Open No. 2001-273900 (claims and others)    Non-Patent Document 1: Thackeray, “Understanding MnO2 for lithium batteries” (material for the lecture at IBA Inuyama Meeting, Oct. 28 and 29, 1991), pp. 33, 35, 36